fontselect: check fontprovider constructors for failure
fontselect: check fontprovider constructors for failure

Should fix the DirectWrite to Fontconfig fallback.

sanyaade-g2g-repos/libass,libass/libass,mwgoldsmith/libass,sanyaade-g2g-repos/libass,ShiftMediaProject/libass,Akemi/libass,grigorig/libass,xbmc/libass,torque/libass,Akemi/libass,MrSmile/libass,astiob/libass,MrSmile/libass,stps/libass,libass/libass,grigorig/libass,sanyaade-g2g-repos/libass,astiob/libass,xbmc/libass,Akemi/libass,stps/libass,torque/libass,stps/libass,mwgoldsmith/libass,mwgoldsmith/libass,ShiftMediaProject/libass,torque/libass